For the purpose of better understanding the present invention it is important to recognize prior practice when employing a typical rotary bender and its cooperating die section in a press brake, by way of example.
In the usual set up, a rotary bending tool or bender is attached to the ram of a press brake for movement toward and away from a cooperating forming anvil of a die section for the purpose of folding or bending sheet material between the bender and the anvil. In general such rotary benders are capable of bending sheet material of varying thicknesses. For example, one typical standard size rotary bender to be referred to hereinafter is designed to bend sheet material having a prescribed minimum thickness of 0.010 inches and a maximum thickness of 0.042 inches.
To accomplish such thickness changes, the die section is made up of a base secured to the bed of the press. The base has a forming anvil with which the rotary bender cooperates. A heel plate is movably connected to on side of the base and has a machined face designed to engage an opposing precision ground surface at one end of a saddle member which supports the rotatable rocker of the bending tool. When set up to handle material of the recommended minimum thickness for a particular bender the opposing surfaces of the heel plate and saddle member are engaged and located at a precise dimension from the vertical center line of the rotary bender which is aligned with the center line of the die section and press ram.
When the bender and die section are aligned to handle thicker materials, say at the recommended maximum thickness for the particular size rotary bender noted above, the heel plate surface is disengaged and moved away from the precision ground surface of the rotary bender's saddle. This insures proper material thickness clearance between the bender rocker and an opposing end surface of the forming anvil with which the bender rocker works. In order to maintain proper clearance between the bender rocker and the base forming anvil working edge, it is necessary to add an appropriate shim between the heel plate and the base; the shim being of a selected thickness to accommodate the added material thickness between the rocker and the end face of the forming anvil. Once the shim is in position the heel plate is again locked tightly in place against the shim.
Unfortunately, the addition of the shim between the heel plate and the base of the die section, causes the base and its mounting tang to shift laterally off the center line of the press, as well as out of alignment with the bender unit assembly. This condition is completely unacceptable and can seriously damage both the press and bending tool. Additionally, any parts produced under these operating conditions would likely have inaccurate and inconsistent bends in the finished parts and possibly could endanger the press operator.
According to the above described procedures and practice each and every change in material thickness requires a different shim thickness and complete realignment of the die section in the press.
To accomplish this change the die holder is loosened and moved to a position where both halves of the bending tool are properly aligned in the press even if such alignment means that the forming anvil and the die holder are aligned off the center line of the press. Thereafter, the die holder is re-tightened and rechecked to assure its proper alignment after the tightening procedure.
When one considers that most common press brake die holders are 12 feet long, it is quite apparent how time consuming and expensive this entire procedure can be. When it is further considered that there are as many as 13 different thicknesses of standard gauge sheet steel available between thinnest and thickest gauge and the same number of thicknesses if one is bending galvanized steel, stainless steel, aluminum, brass, etc., the time and expense devoted to proper press alignment under current practice is staggering.